[ganbatekudasai]

No it's not, it's a false equivalence. What the original commenter described has way more pathologies than "startups are hard", and it does not smell like success to me. To pick up on your analogy, it's more like a rock that has been drenched in poop by someone, and you're supposed to use it to cut your food. There are other sharp rocks around, and most of them are not covered by poop, so you might be able to cut your food with it without getting a terrible disease and puke all food out again in the process.

[inconceivable]

okay, so your position is that he should leave because everyone is too mean. that's valid.

[ganbatekudasai]

Don't put words in my mouth. OP mentioned significant equity and the possibility to be acquired, without any details. This could both provide them with something to show after enduring all the suck, as well as with a real chance of changing management. If the question was to join the company, or no equity was at play (including if there's either no realistic chance of that equity being worth something, or if the equity does not lose its value for OP after quitting anyway), then yes, likely best to leave immediately.

Simplistic phrases are not going to help in complex situations with lots of details.

> because everyone is too mean.

No, because it sounds like a business bordering on dysfunction. You should know the difference.

[inconceivable]

> because it sounds like a business bordering on dysfunction

yeah, that's what a startup is.